1. Field of the Invention
This invention relates to the preparation of alkyl substituted bicycloheterocyclic compounds and more particularly pertains to a novel catalytic liquid phase process for the preparation of C-alkyl and C-polyalkyl substituted diazabicyclo-(2,2,2)-octanes, commonly referred to as C-alkyl-triethylenediamines.
2. Prior Art
Triethylenediamine is an exceptional urethane catalyst owing to the presence of two bridgehead nitrogens in the molecule. However, many times it is advantageous to substitute one or more of the ring carbons with an alkyl group in order to match solubility of constituents, increase ease of handling, reduce activity, or reduce the volatile nature of the odoriferous catalyst. C-alkyl and C-polyalkyl triethylenediamines are thus very useful as catalysts and accelerators for urethane systems.
There are several procedures known for the preparation of C-alkyl substituted diazabicyclo-(2,2,2)-octanes by catalytically cyclizing certain substituted piperazine compounds, such as N-hydroxyethyl-methylpiperazines, N,N'-dihydroxyethylmethylpiperazines, etc., in the presence of very specific types of catalysts. Generally, such known procedures are vapor phase reactions which are carried out by contacting the vapors of the substituted piperazine feedstock employed with the acidic-type catalyst at temperatures in excess of about 250.degree. C to about 550.degree. C. For example, U.S. Pat. No. 3,167,518 to Farkas et al discloses a method for preparing 2-methyl diazabicyclo-(2,2,2)-octane by cyclo-dehydrating the reaction product of 2-methylpiperazine with at least an equal molar quantity of ethylene oxide in vapor phase over an active silicious cracking catalyst. More particularly, it is disclosed that the vapor phase cyclodehydration reaction is carried out by passing the ethoxylated 2-methylpiperazine reaction product vapors over a silica-alumina cracking catalyst at a temperature of 325.degree. C to 425.degree. C.
U.S. Pat. No. 3,297,701 to Brader, Jr., et al discloses that C-substituted diazabicyclo-(2,2,2)-octanes may be synthesized by the process of contacting a substituted piperazine compound, such as N-aminoethyl-C-alkyl-piperazines, N-hydroxyethyl-C-alkyl-piperazines, etc., in vapor phase with a metal phosphate catalyst in the presence of ammonia at a reaction temperature within the range of 250.degree. C to about 550.degree. C. In addition, U.S. Pat. No. 3,342,820 to Brader, Jr., teaches a catalytic vapor phase process for synthesizing C-alkyltriethylenediamines employing complex phosphates as catalysts which contain in their crystalline structure an alkali metal and a trivalent element such as aluminum, boron, bismuth and iron. It is disclosed in the patent that the complex phosphate catalyst is very specific in the process for the preparation of C-alkyl-triethylenediamines. More particularly, the disclosed process is described as being carried out in vapor phase which includes passing the described substituted piperazine feedstock vapors over the complex phosphate catalyst along with ammonia at a temperature within the range of about 250.degree. C to 550.degree. C.
However, conventional vapor phase catalytic processes for preparing C-alkyl-triethylenediamines usually suffer from one or more of several disadvantages. For example, under the conventional vapor phase reaction conditions employed, several competing side reactions occur resulting in crude reaction product effluents which contain several undesirable by-products such as piperazine, pyrizenes, etc. Not only do such side reactions deleteriously affect the yield of the desired product, but also the by-products formed have physical properties substantially similar to the desired products. These substantially similar physical properties make it extremely difficult to separate the desired C-alkyl-triethylenediamines in pure form from the crude reaction product effluent.
U.S. Pat. No. 3,080,371 to Spielberger et al describes a liquid phase process for preparing triethylenediamine which includes heating N-hydroxyethyl piperazine or N,N'-dihydroxyethyl piperazine with a high boiling carboxylic acid catalyst in the presence of a high-boiling point solvent at temperatures between 250.degree. and 350.degree. C. The disclosed process employs temperatures lower than those normally employed in the above-mentioned vapor phase processes. However, the process has been found to be very slow and usually results in the formation of excessive amounts of a polymeric residue. In addition, the liquid phase process described in U.S. Pat. No. 3,080,371 is specifically directed to the preparation of triethylenediamine employing feedstocks of N-hydroxyethyl piperazine or N,N'-di-hydroxyethyl piperazine. It has been demonstrated, as described in the aforementioned U.S. Pat. No. 3,342,820 to Brader, Jr., that the catalyst requirements for making C-substituted triethylenediamines are quite different from the catalyst requirements for making triethylenediamine. Experimentation has shown that C-alkyltriethylenediamines or their precursors are more sensitive than triethylenediamine or its precursors and that unpredictably different degrees of response of initial feedstocks with different catalysts occur.
It has now been discovered that certain acidic phosphorus compounds can be used to effect a new catalytic process for preparing C-alkyl-triethylenediamines, in the liquid phase providing high selectivity and good yields of the desired product. Since the process of the instant invention is carried out in liquid phase, it does not suffer from many of the aforementioned disadvantages accompanying conventional vapor phase processes. In addition, in the invention process a novel catalyst system is employed which heretofore has not been suggested in the literature.